Many medically significant biological processes result from signal transduction pathways that involve G-proteins and their downstream effector molecules. Numerous drugs antagonize binding between a GPCR and its activating ligand. Due to its unique mechanism via proteolytic generation of a tethered ligand, which is then present at molar concentrations, it has been difficult to develop or discover antagonists for the thrombin receptor (PAR-1). The investigators have explored an alternative possibility, that of antagonizing the receptor G-protein interface. The investigators screened a combinatorial library to identify peptides that bind activated PAR-1. The goal of this project is to: a) assess the binding affinity of the peptides, b) determine their ability to block the receptor G-protein interaction, and c) analyze them in vivo for their ability to inhibit thrombin mediated endothelial activation, including cell permeability. By obtaining a rank order of potency for the high affinity peptides, the investigators can efficiently identify small molecules in subsequent screening. This two-step approach will potentially lead to the discovery of a new class of post-receptor thrombin inhibitors. Given the role of thrombin in endothelial barrier function, they feel antagonists of the PAR-1-G protein interface may be useful in treating diseases where there is endothelial permeability dysfunction, including ARDS. PROPOSED COMMERCIAL APPLICATION: NOT AVAILABLE